Use of NN′-isopropylidene dipeptides in peptide synthesis
The direct condensation of dipeptides with acetone has been found generally useful for the preparation of 2-(2,2,4-trialkyl-5-oxoimidazolidin-1-yl)alkanoic acids. Peptide synthesis using these NN′-isopropylidene dipeptides may be conveniently carried out with dicyclohexylcarbodi-imide; such couplings are racemisation-free even in the absence of additives. Subsequent deprotection may be effected by hydrolysis under neutral conditions. If required. NN′-isopropylidene dipeptides may be stabilised temporarily towards hydrolysis by conversion into their N-benzyloxycarbonyl or N-nitroso-derivatives.